Lyle Thurston was a founding member of Greenpeace, one of the dozen Canadian or Canada-based anti-war activists who sailed a mackerel-fishing boat up the North Pacific to Alaska in 1971 to try to prevent a US nuclear test. They "failed", but only in the sense that the test eventually went ahead.

Their success was in forcing its postponement, in embarrassing the United States into ending underground tests and not least in giving birth to an international movement, Greenpeace, which would lead the way in the fight to save whales, seals and rainforests, and to reduce global warming.

Not bad for a bunch of peacenik "love children" who described themselves as "a convergence of hippies, draft dodgers, Tibetan monks, seadogs, artists, radical ecologist, rebel journalists, Quakers and expatriate Yanks". Lyle Thurston was a pharmacist and doctor, though that's not to say he wasn't one or more of the above, certainly a hippie, a radical ecologist and a rebel who preferred ballet and opera in an era of rock. While living in a commune of doctors and lawyers in Deep Cove, north of Vancouver, in a house they called "the party mecca", he became widely known as "the Doc" after he took to setting up a makeshift, free-of-charge medical tent at rock concerts to treat kids who had overdosed. It was the Sixties. He was kept busy.

He bumped into the radical, visionary journalist Bob Hunter and a group of similarly minded anti-war activists in the Cecil Hotel bar on Granville Street, Vancouver, in 1969, at the height of the Vietnam war. Fearing that nuclear tests in the North Pacific could cause a devastating tsunami, they called themselves the "Don't Make a Wave" committee, using a single pay phone by the bar's pool table to get their message to the Canadian media, who at first dubbed them "eco-freaks".

When the group heard the US Department of Defence planned a five-megaton nuclear bomb test under the Aleutian island of Amchitka in Alaska, they decided to "bear witness", as their Quaker members put it, and to "launch a mind bomb" that would attract world attention. They would rent a boat and head for the test zone, but they would need a doctor on board, and a pharmacist, in case of emergencies, seasickness, or, as it inevitably turned out, hangovers. "Doc Thurston" was the perfect candidate, and only too eager for a challenge. He had spent the first years of his medical practice attending to Cree Indian patients on a reservation. In Vancouver, he had been involved in a project to help young drug addicts. He was also something of an expert on LSD dosage, having volunteered for an "acid experiment" as part of his university course.

After sympathetic musicians including Joni Mitchell and James Taylor raised $20,000 at a special gig, Thurston put a "Back Soon" sign on the door of his surgery and headed for Vancouver harbour.

On 15 September 1971, a motley crew of "long-haired, bearded weirdos with shoulder bags" – their own description – set sail on a mackerel seiner called the Phyllis Cormack, named after the wife of its captain. Essentially, they were children of CND, the Campaign for Nuclear Disarmament, concerned about what a nuclear test could do not just to humans, but to the environment, so they billed themselves as "green". One of them, Bill Darnell, suggested they should combine their two aims – "peace" and "green". So they changed the ship's name to Greenpeace, hoisted a hand-made flag carrying that word and the peace symbol and sailed off, unknowingly to make history.

In the words of Hunter, the group's "spiritual guru", who died in 2005, "It is incredible that we eco-freaks should be moving out in an assault on the power that put men on the moon, that could blow up the world, in this boat Greenpeace, in her other life the Phyllis Cormack." According to Hunter, "Doctor Feelgood," as the crew took to calling Thurston, was "about as far into existentialism and phenomenology as you can get without being locked up".

That diagnosis proved accurate when Hunter was at the helm in what they called the "Penthouse" of the Greenpeace – the bridge – and Thurston was "navigating", using cassettes of Beethoven's Fifth and the Moody Blues' On the Threshold of a Dream as inspiration. The bad news was that the cassette player was too close to the ship's compass and knocked them off course by 90 miles. The good news, for them, was that US Coastguard vessels lost track of them for days and had to scramble a Hercules aircraft to find them.

The vessel was boarded and detained by the coastguard in late September 1971. Publicity surrounding its voyage delayed the US test but it finally went ahead on 6 November, at close to five megatons the biggest underground nuclear test in US history, but also its last as worldwide opposition grew. The Greenpeace Foundation, root of the current Amsterdam-based Greenpeace International, was formally founded in Vancouver in May 1972 and Thurston was a prime mover in the opening of a London branch.

Although Thurston was understandably proud of that first seagoing mission, one that changed all our lives, it was far from his only achievement. He was born in the small French-speaking town of Sainte Rose du Lac, Manitoba in 1937, but was brought up and went to school in Yorkton, Saskatchewan. He graduated from the medical college of the University of Saskatchewan in 1960 and as an MD in 1967, moving to Vancouver to set up a practice after an internship in Toronto.

In the years after the first Greenpeace voyage, Thurston joined the group's campaign against French nuclear testing in the South Pacific. It was during that campaign, in 1972, that the increasingly influential Greenpeace group was invited to the Vatican for what Thurston assumed was an audience with Pope Paul VI. When he realised there were 2,000 other invitees, Thurston, who had smuggled in the original Greenpeace flag inside his coat, slipped outside for a cigarette. The Vatican's Swiss Guard wouldn't let him back in but, when the Pope emerged into a courtyard, Thurston pulled out the flag and the Pope duly blessed it. "Good," said one of his colleagues later. "We've just gained 700 million new members."

Thurston later joined the anti-whaling movement, notably with the more militant Sea Shepherd Conservation Society, which would eventually fall into conflict with Greenpeace over how far protest should go. "The Doc" managed to stand above the often childish wrangling between the two groups and later travelled the world as both ecologist and physician. His love of ballet, and friendship with dancers such as Wayne Eagling, won him the job of official physician to the Royal Ballet during some of its tours, including to China.

Over the past few years, in retirement, Thurston lived on Wickaninnish Island, off the west coast of Canada, pretty remote, but not enough so to keep friends from around the world from popping in to "drink like Hemingway", as he liked to put it.